In recent years, it has been demonstrated that one of the most effective means of disabling a military adversary's air strike capability is to destroy the runways from which the adversary's aircraft must operate. This has led to the development of munitions having a sole purpose of inflicting damage to runways. Damage to runways inflicted by such special purpose munitions and other types of munitions varies from cratering caused by direct hits by pavement-penetration bombs, to surface pitting and spalls caused by aircraft cannon fire.
It is, of course, highly desirable to repair a damaged runway as quickly as possible in order to permit its use. At the present time, the most expedient means of repairing a damaged runway is considered to be filling and covering bomb craters and clearing debris from the runway without attempting repair of surface pitting and spalls. Covering a bomb crater in a reasonably short period of time and achieving a perfectly flat surface at the repair site is not possible. Therefore, expediently repaired runways include both surface pitting and spalls, and nonflat crater repair sites. If such a runway is to be usable by military aircraft, the aircraft must be provided with load isolation capability sufficient to enable the aircraft to land on the runway and taxi over surface damage and crater repair sites. Conventional shock absorbers associated with the landing gear on military aircraft do not have sufficient load isolation capability to protect the aircraft structure from excessive rough field taxi loads and to control the pitch and heave motion of the aircraft during ground roll over an expediently repaired runway.
It is anticipated that future military aircraft will be required to land at vertical velocities, or sink rates, significantly higher than the landing sink rates of current military aircraft. Higher sink rates will in turn create a need for more efficient absorbtion of touchdown energy in order to protect an aircraft from loads exceeding its structural limits. Thus, future shock absorbers for the landing gear of military aircraft will be required to more efficiently absorb touchdown energy.
The requirements for future military aircraft discussed above, the need for controlling rough field taxi loads and aircraft motion during ground roll and the need for more efficient absorbtion of touchdown energy, are, in combination, incompatible with conventional landing gear designs and cannot be achieved with such designs. Although conventional landing gear generally absorbs touchdown energy with reasonable efficiency, conventional landing gear does not provide the load isolation capability and control of aircraft motion necessary for ground roll operations over rough surfaces. Modification of conventional landing gear to improve ground roll operation cannot be achieved using conventional design approaches without adversely affecting landing performance. Therefore, there is a need for an entirely new design approach.
A shock absorber is disclosed in each of U.S. Pat. No. 2,332,161, granted Oct. 19, 1943, to B. D. McIntyre et al; U.S. Pat. No. 2,426,585, granted Sept. 2, 1947, to H. S. Bean et al; U.S. Pat. No. 2,655,232, granted Oct. 13, 1953, to M. D. Etherton; U.S. Pat. No. 2,958,400, granted Nov. 1, 1960, to E. D. Gilbert; U.S. Pat. No. 3,207,270, granted Sept. 21, 1965, to J. T. Ellis, Jr.; U.S. Pat. No. 3,344,894, granted Oct. 3, 1967, to G. F. Kenworthy; U.S. Pat. No. 3,419,114, granted Dec. 31, 1968, to R. D. Rumsey; U.S. Pat. No. 3,446,317, granted May 27, 1969, to B. Gryglas; U.S. Pat. No. 3,478,846, granted Nov. 18, 1969, to H. S. Germond IV; U.S. Pat. No. 3,510,117, granted May 5, 1970, to H. W. Scholin et al; U.S. Pat. No. 3,598,206, granted Aug. 10, 1971, to R. J. Hennells; U.S. Pat. No. 3,605,960, granted Sept. 20, 1971, to J. R. Singer; U.S. Pat. No. 3,693,767, granted Sept. 26, 1972, to K. B. Johnson; U.S. Pat. No. 3,750,856, granted Aug. 7, 1973, to G. F. Kenworthy; U.S. Pat. No. 3,998,302, granted Dec. 21, 1976, to W. J. Schupner; and U.S. Pat. No. 4,057,129, granted Nov. 8, 1977, to R. J. Hennells. The shock absorbers disclosed by Bean et al, Etherton, and Gilbert are specifically intended for use in aircraft landing gear. U.S. Pat. No. 3,531,065, granted Sept. 29, 1970, to R. J. Brown discloses an aircraft arresting device for use on aircraft carriers, which device has a hook arm controlled by a telescopic jack and damper unit.
In the shock absorbers disclosed by Ellis, Jr., Kenworthy (both patents), Rumsey, Gryglas, Germond IV, Scholin et al, Hennells (both patents), Singer, Johnson, and Schupner, axially spaced openings in a metering tube or cylinder are progressively closed off by a piston element as the shock absorber compresses to provide increasing resistance to the compressive movement. The shock absorbers disclosed by Scholin et al, Johnson, and Schupner each include a metering sleeve that is coaxial with the cylinder and manually movable in an axial direction to adjust the effective size of the openings in the cylinder. The shock absorbers disclosed in the 1967 Kenworthy patent, the Germond IV patent, and the 1971 Hennells patent also have coaxial metering sleeves for adjusting the effective size of the openings in the cylinder, but the manual adjustment is accomplished by rotating the sleeve. Ellis, Jr., and Gryglas disclose other means for manually adjusting the effective size of the openings in the metering tube. The Rumsey shock absorber is provided with an adjustment screw for adjusting a valve to in turn adjust the stiffness of the shock absorber. In operation, the valve automatically maintains a fixed pressure differential across the metered orifice area.
The Singer patent, the 1973 Kenworthy patent, and the 1977 Hennells patent each disclose a sleeve that is coaxial with the metering tube and slides axially with respect to such tube to automatically adjust the effective area of the openings in the tube. In each of the three devices, the metering sleeve is spring-biased and moves in response in changes in pressure. In the Singer and Kenworthy shock absorbers, higher pressure during the compression stroke causes the sleeve to move to automatically throttle the openings to in turn provide greater resistance to compressive movement; in the Hennells shock absorber, higher pressure during the compression stroke causes the sleeve to be axially displaced to automatically increase the hydraulic flow path cross section.
The shock absorber disclosed by McIntyre et al includes a cylinder with a plurality of axially spaced sets of orifices that are controlled by valves of differing resistance. When either compression or extension movement of a piston within the cylinder is greater than normal, a set of openings is closed so that hydraulic fluid must flow through valves with greater resistance. This automatically provides greater resistance to movement that is greater than normal. In the Etherton shock absorber, a hollow metering pin carried by one tubular member slides through a radial sealing wall carried by another tubular member, and the rate of flow of hydraulic fluid is controlled by apertures in the pin passing the sealing wall. During compression, there is at first high resistance, then the resistance decreases quickly, and then the resistance again gradually increases. In the Gilbert shock absorber, the changing diameter of a metering pin moving past a diaphragm provides changing resistance similar to that in the Etherton shock absorber. The contraction of the shock absorber compresses air in the shock absorber to provide a resilient cushion of compressed air which supports the aircraft and absorbs part of the jarring and bumping of the aircraft during taxiing.
The above patents and the prior art that is discussed and/or cited therein should be studied for the purpose of putting the present invention into proper perspective relative to the prior art.